Autosomal Dominant, Autosomal Recessive Inheritance Simple Qs

What is a pedigree?

A graphical representation of family history; essential for genetic evaluation and research

What information should be collected in a pedigree?

Names/initials, birth/death dates, health conditions, causes of death, genetic test results, ethnic background, other relevant info

What are pedigrees used for?

Diagnosis, testing strategy, inheritance patterns, risk calculation, reproductive options, education, rapport

What is Mendel's principle of segregation?

Genes occur in pairs; only one transmitted to offspring; remain intact across generations

What is Mendel's principle of independent assortment?

Genes at different loci transmitted independently; traits not inherited as a package

What are features of autosomal dominant inheritance?

Vertical pattern, phenotype in every generation, 50% recurrence risk, affected parent present, male-to-male transmission possible

What are features of autosomal recessive inheritance?

Horizontal pattern, 25% recurrence risk, usually unaffected parents, equal sex ratio, more likely with consanguinity

What is quasidominant inheritance?

When affected individual with AR disorder mates with carrier; recurrence risk 50%

What is achondroplasia inheritance pattern?

Autosomal dominant; homozygotes have more severe phenotype

What happens with one vs two BRCA2 mutations?

One mutation = HBOC. Two mutations = Fanconi anemia with marrow failure and tumors

What is allelic heterogeneity?

Different mutations in same gene cause different phenotypes (e.g., isolated growth hormone deficiency)

What is locus heterogeneity?

Different genes cause same phenotype (e.g., Lynch syndrome, OI, PKD)

What is pleiotropy?

One gene affects multiple systems (e.g., Marfan syndrome)

What is incomplete dominance?

Heterozygotes show blended phenotype (e.g., red+white flowers=pink)

What is codominance?

Both alleles expressed equally (e.g., ABO blood group, calico cats)

What is a de novo mutation?

New mutation in child; neither parent affected; recurrence risk low for siblings but 50% for offspring

What is germline mosaicism?

Mutation in subset of parental germ cells; parent unaffected; multiple affected offspring possible

What is reduced penetrance?

Not all mutation carriers show phenotype; may appear to skip generations (e.g., BRCA, retinoblastoma)

What is age-dependent penetrance?

Phenotype develops later in life (e.g., Huntington's disease)

What is variable expression?

Same mutation shows different severity/symptoms (e.g., NF1)

What is coefficient of relationship?

1st degree = 50% (parents, children, sibs). 2nd degree = 25% (aunts, uncles, grandparents). 3rd degree = 12.5% (first cousins)

How does consanguinity affect recessive inheritance?

Increases chance of shared mutations; higher risk of AR disease; first-cousin marriages raise probability